Protective effect of Allium sativum (garlic) aqueous extract against lead-induced oxidative stress in the rat brain, liver, and kidney

The present investigation was undertaken to evaluate the ameliorative activity of Allium sativum against lead-induced oxidative stress in the brain, liver, and kidney of male rats. Four groups of male Wistar strain rats (100-120 g) were taken: group 1 received 1000 mg/L sodium acetate and group 2 was given 1000 mg/L lead acetate through drinking water for 2 weeks. Group 3 and 4 were treated with 250 mg/kg body weight/day of A. sativum and 500 mg/kg body weight/day of A. sativum, respectively, by oral intubation for a period of 2 weeks along with lead acetate. The rats were sacrificed after treatment and the brain, liver, and kidney were isolated on ice. In the brain, four important regions namely the hippocampus, cerebellum, cerebral cortex, and brain stem were separated and used for the present investigation. Blood was also drawn by cardiac puncture and preserved in heparinized vials at 4 °C for estimation of delta-aminolevulinic acid dehydratase (ALAD) activity. The results showed a significant (p < 0.05) increase in reactive oxygen species (ROS), lipid peroxidation products (LPP), total protein carbonyl content (TPCC), and lead in the selected brain regions, liver, and kidney of lead-exposed group compared with their respective controls. Blood delta-ALAD activity showed a significant (p < 0.05) decrease in the lead-exposed rats. However, the concomitant administration of A. sativum resulted in tissue-specific recovery of oxidative stress parameters namely ROS, LPP, and TPCC. A. sativum treatment also restored the blood delta-ALAD activity back to control. Overall, our results indicate that A. sativum administration could be an effective antioxidant treatment strategy for lead-induced oxidative insult.

Mechanism of c-Met and EGFR tyrosine kinase inhibitor resistance through epithelial mesenchymal transition in non-small cell lung cancer

According to currently available estimates from Cancer Research UK, 14.1 million new lung cancer cases were diagnosed and a staggering 8.2 million people worldwide died from lung cancer in 2012. EGFR and c-Met are two tyrosine kinase receptors most commonly overexpressed or mutated in Non-small Cell Lung Cancer (NSCLC) resulting in increased proliferation and survival of lung cancer cells. Tyrosine kinase inhibitors (TKIs), such as erlotinib, approved by the FDA as first/second line therapy for NSCLC patients have limited clinical efficacy due to acquired resistance. In this manuscript, we investigate and discuss the role of epithelial mesenchymal transition (EMT) in the development of resistance against EGFR and c-Met TKIs in NSCLC. Our findings show that Zeb-1, a transcriptional repressor of E-Cadherin, is upregulated in TKI-resistant cells causing EMT. We observed that TKI-resistant cells have increased gene and protein expression of EMT related proteins such as Vimentin, N-Cadherin, β-Catenin and Zeb-1, while expression of E-Cadherin, an important cell adhesion molecule, was suppressed. We also confirmed that TKI-resistant cells display mesenchymal cell type morphology, and have upregulation of β-Catenin which may regulate expression of Zeb-1, a transcriptional repressor of E-Cadherin in TKI-resistant NSCLC cells. Finally, we show that down-regulating Zeb-1 by inducing miR-200a or β-Catenin siRNA can increase drug sensitivity of TKI-resistant cells.

Current Molecularly Targeting Therapies in NSCLC and Melanoma

Surgery, radiation therapy, and chemotherapy are the traditional options to control tumor progression. However, these strategies are fraught with harmful side effects and are ineffective in metastatic and advanced cancers. Biomarkers that are overexpressed in cancers and are involved in cell growth, proliferation, migration, and survival have recently become the focus of new molecular targeting therapies. Novel therapies targeting biomarkers have roles in tumorigenesis that are overexpressed in cancers may be more efficacious and less toxic in comparison to traditional therapies. These therapies include the use of tyrosine kinase inhibitors and monoclonal antibodies for the treatment of cancer. However, the efficacy of these therapies is limited due to the development of drug resistance after prolonged treatment. Current research is focused on understanding mechanisms of resistance to overcome the barriers limiting the use of these targeting therapies in the treatment of cancer. In this review, we will discuss the clinical status of tyrosine kinase inhibitors and monoclonal antibodies against several prevalent biomarkers that are candidates for therapy in non-small cell lung cancer (NSCLC) and melanoma.

Abstract 347: Mechanism of c-Met TKI resistance and role of epithelial mesenchymal transition in melanoma

Various tyrosine kinase inhibitors (TKI’s) are approved for the treatment of melanoma, but their efficacies are limited due to development of drug resistance. To analyze the resistance to c-Met inhibitors we used two melanoma cell lines: MU which has mutated BRAF (V600E +ve) and RU which has wild type BRAF. These cell lines were also made resistant to c-Met inhibitor, SU11274 by growing them in progressively increasing concentrations of drug.

In earlier studies we observed activation of Wnt pathway in both of the aforementioned cell lines indicating the role of active β-Catenin in transcription and hence cell proliferation. β-Catenin levels when localized and accumulated in the nucleus binds to TCF/LEF and activates transcription. The level of β-Catenin in the cytosol is regulated by the adherens junction proteins (E-Cadherin) along with the Wnt pathway. Increased levels of β-Catenin might be a possible result of loss of E-Cadherin which is related to epithelial mesenchymal transition. During epithelial mesenchymal transition (EMT) cells transition from epithelial (attached, non-migratory) to mesenchymal (unattached and migratory) cells which promotes metastasis.

We examined the role of EMT in the development of resistance in the c-Met TKI resistant melanoma cell lines. We quantified the β-Catenin activity using luciferase assay and observed a 5 fold upregulation in the SU11274 resistant MU cells when compared to MU parental cells in the presence of HGF. Additionally, we performed immunoblotting, where we observed modulation in EMT related proteins in MU and RU parental and resistant cells. E-Cadherin, ZO-1, Claudin-1 and Slug were found to be downregulated 1.5 - 2.7 fold, 1.5 - 2.0 fold, 2 - 9 fold and 1.5 - 2 fold respectively and N-Cadherin and β-Catenin were found to be upregulated 1.8 - 5.3 and 2.4 - 3.7 fold respectively in the SU11274 resistant MU cells in the presence and absence of HGF and SU11274 treatments. Similarily we observed upregulation of β-Catenin by 1.7 fold and downregulation of E-Cadherin and ZO-1 by 2 - 3.5 fold and 6 - 9 fold respectively in SU11274 resistant RU cells when compared to RU parental cells in the presence and absence of HGF and SU11274 treatments. Further studies are being carried to understand the role of EMT in the development of this acquired resistance.

These results may help in development of novel therapies for melanoma patients or may help in increasing the efficacy and beneficence from the currently available therapeutics.

Citation Format: Supriya Rajanna, Ichwaku Rastogi, Sunil Palani, Neelu Puri. Mechanism of c-Met TKI resistance and role of epithelial mesenchymal transition in melanoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 347. doi:10.1158/1538-7445.AM2015-347

Targeting c-Met in melanoma: mechanism of resistance and efficacy of novel combinatorial inhibitor therapy

Numerous tyrosine kinase inhibitors (TKIs) targeting c-Met are currently in clinical trials for several cancers. Their efficacy is limited due to the development of resistance. The present study aims to elucidate this mechanism of c-Met TKI resistance by investigating key mTOR and Wnt signaling proteins in melanoma cell lines resistant to SU11274, a c-Met TKI. Xenografts from RU melanoma cells treated with c-Met TKIs SU11274 and JNJ38877605 showed a 7- and 6-fold reduction in tumor size, respectively. Resistant cells displayed upregulation of phosphorylated c-Met, mTOR, p70S6Kinase, 4E-BP1, ERK, LRP6, and active β-catenin. In addition, GATA-6, a Wnt signaling regulator, was upregulated, and Axin, a negative regulator of the Wnt pathway, was downregulated in resistant cells. Modulation of these mTOR and Wnt pathway proteins was also prevented by combination treatment with SU11274, everolimus, an mTOR inhibitor, and XAV939, a Wnt inhibitor. Treatment with everolimus, resulted in 56% growth inhibition, and a triple combination of SU11274, everolimus and XAV939, resulted in 95% growth inhibition in RU cells. The V600E BRAF mutation was found to be positive only in MU cells. Combination treatment with a c-Met TKI and a BRAF inhibitor displayed a synergistic effect in reducing MU cell viability. These studies indicate activation of mTOR and Wnt signaling pathways in c-Met TKI resistant melanoma cells and suggest that concurrent targeting of c-Met, mTOR, and Wnt pathways and BRAF may improve efficacy over traditional TKI monotherapy in melanoma patients.

Lead induced alterations in nitrite and nitrate levels in different regions of the rat brain

Nitric oxide (NO) is a free radical synthesized by nitric oxide synthase (NOS) during the conversion of L-arginine to citrulline. Lead (Pb) affects neuronal functioning in the rat brain. Nitric oxide, a neuronal messenger has a short half life and converts immediately into nitrite and nitrate. The present study is designed to determine lead-induced alterations in NO production by measuring nitrite and nitrate in the cerebellum, the hippocampus, the frontal cortex and the brain stem of the rat brain. Male Sprague-Dawley rats were treated with lead acetate (5 and 15 mg/kg body wt.) by intraperitoneal injection. The control and experimental rats were sacrificed at the end of 7 and 14 days after treatment and different regions of the brain were isolated. Nitrite and nitrate (NOx) levels were estimated by the chemiluminescent method using the NOA 280 (Sievers). The data suggested dose-dependent and region-specific responses to lead. Both treatments of lead reduced NOx levels in the cerebellum and the hippocampus. However, the frontal cortex and the brain stem responded differently to Pb exposure. NOx levels in the frontal cortex were significantly increased in rats treated with low and high doses of Pb for 7 days but not in rats treated for 14 days, whereas in the brain stem, NOx levels were increased in a dose- and time-dependent manner. Although, the response was time-dependent, the variation between 7- and 14-day treatment was not clearly delineated. These results provide additional evidence that Pb exposure alters NO-production in rat brain leading to neuronal dysfunction.

Interaction of metals with muscarinic cholinoceptor and adrenoceptor binding, and agonist-stimulated inositol phospholipid hydrolysis in rat brain

In vitro mercury (Hg) or lead (Pb) effectively inhibited the binding of 3H-quinuclidinyl-benzilate (QNB) (a muscarinic cholinoceptor antagonist) and 3H-prazosin (an alpha 1-adrenoceptor antagonist) to their receptors in cerebellar and cerebral cortex membranes in a concentration-dependent manner. Hg was more potent than Pb. When the rats were treated with Hg (5 mg/kg body wt) or Pb (25 mg/kg body wt) for 24 hr, a decrease in 3H-prazosin and an increase in 3H-QNB receptor binding were observed in cerebral cortex. There was no alteration in 3H-prazosin binding in cerebellum with the above treatment of metals, but 3H-QNB binding in cerebellum was significantly inhibited by Hg. However, both 3H-prazosin and 3H-QNB receptor bindings were significantly decreased in cerebellum of rats treated for 7 days with Hg (1 mg/kg body wt/day) or Pb (25 mg/ kg body wt/day). But in cerebral cortex of rats treated with these metals for 7 days, a decrease in 3H-prazosin and an increase in 3H-QNB receptor binding activities were noticed. There was a significant decrease in phospholipid content in cerebral cortex but not in cerebellum of rats treated with these metals for 7 days. At 100 microM concentration carbachol or acetylcholine or norepinephrine stimulated 3H-inositol incorporation and 3H-inositol phosphate (IP) formation in rat cerebral cortical slices. Hg or Pb in vitro though increased the agonist-stimulated 3H-inositol incorporation, 3H-IP formation was not significantly altered. The present investigation demonstrates the differential responses by alpha 1-adrenoceptor and muscarinic cholinoceptor in cerebellum and cerebral cortex of rat to in vitro and in vivo effects of Hg or Pb.

In vitro metal inhibition of N-methyl-D-aspartate specific glutamate receptor binding in neonatal and adult rat brain

The in vitro effect of methyl mercury (MM) and lead (Pb) on N-methyl-D-aspartate (NMDA)-specific glutamate receptor binding in neonatal (10 days old) and adult rat brain was investigated. The cerebral cortex was isolated from the neonatal and adult male Sprague-Dawley rats and the synaptic plasma membranes were prepared to study the NMDA-specific glutamate receptor binding by using (3H)-glutamic acid. The metal salts such as methyl mercury chloride and lead acetate were used to study the effect of MM and Pb. Both MM and Pb significantly inhibited the receptor binding in neonatal and adult rat brain in a concentration-dependent manner. MM (IC50:0.95 +/- 0.08 microM) was more potent in inhibiting the receptor binding than Pb (IC50:60 +/- 7 microM) in neonatal rat brain. A similar high potency was observed for MM than Pb in adult rat brain but the IC50 values are very high (70 +/- 6 microM and 300 +/- 24 microM respectively) indicating less effect compared to neonatal brain. The data suggest that NMDA-receptor binding was more sensitive to MM and Pb in neonatal brain than in adult. MM was more effective than Pb because of its more lipophilicity.

In vitro and in vivo effects of lead, methyl mercury and mercury on inositol 1,4,5-trisphosphate and 1,3,4,5-tetrakisphosphate receptor bindings in rat brain

In vitro and in vivo effects of mercury (Hg), methyl mercury (MM) and lead (Pb) on [3H]inositol 1,4,5-trisphosphate (IP3) and [3H]inositol 1,3,4,5-tetrakisphosphate (IP4) receptor binding in the Sprague-Dawley rat brain cerebellar membranes were studied. In vitro studies indicate that binding of [3H]IP3 and [3H]IP4 to cerebellar membranes was inhibited by Hg while they were stimulated by MM or Pb in a concentration-dependent manner. MM was more potent (EC50 3.4 microM) than Pb (EC50 18.2 microM) in stimulating the [3H]IP3 receptor binding activity whereas Pb (IC50 30 microM) was more potent than MM (IC50 133 microM) in stimulating the [3H]IP4 receptor binding. When the rats were treated (i.p) with Hg (5 mg/kg body wt.) or MM (5 mg/kg body wt.) or Pb (25 mg/kg body wt.) for 3 or 24 h, no significant alterations in [3H]IP3 receptor binding were observed in cerebellum and cerebral cortex. But the above treatment of Pb or MM for 3 or 24 h to rats resulted in an increase of [3H]IP4 receptor binding in the membranes of cerebral cortex. However, the rats treated with Hg (1 mg/kg body wt./day) or Pb (25 mg/kg body wt./day) for 7 days did not show any alteration in binding of [3H]IP3 to its receptors in cerebellar membranes but an increase in this receptor binding was noticed with the treatment of MM (2.5 mg/kg body wt./day) for 7 days. The cerebellum and cerebral cortex of rats with the above treatment of MM or Pb for 7 days exhibited an increase in [3H]IP4 receptor binding. These in vitro and in vivo data suggest that alterations in inositol polyphosphate receptor binding by metals could result in alterations in intracellular calcium levels which may influence neuronal activity.

Inhibition of calcium transport by mercury salts in rat cerebellum and cerebral cortex in vitro

The present investigation was initiated to study the differential effects of mercury salts on calcium pump activity of rat cerebellum and cerebral cortex in vitro. The calcium pump activity was studied by assaying calcium-adenosine triphosphatase (Ca(2+)-ATPase) in synaptic plasma membranes (SPMs) and microsomes of cerebellum and cerebral cortex in the presence of different micromolar concentrations of mercury and methylmercury. The 45Ca uptake in microsomes of cerebellum and cerebral cortex was also determined in the presence of both the salts of mercury. The SPMs and microsomes were prepared by differential centrifugation using a sucrose gradient (0.8/1.2 M). The Ca(2+)-ATPase activity was determined by estimating the inorganic phosphate. The 45Ca uptake was measured in microsomes by using 45CaCl2. Calcium-ATPase in SPMs was significantly inhibited by these two mercury salts in a concentration-dependent manner. In cerebellum and cortex, the IC50 values for mercuric chloride were 0.065 and 0.081 microM, respectively, whereas they were 0.354 and 0.384 microM for methylmercury chloride, indicating that mercuric chloride was more potent in inhibiting the plasma membrane Ca2+ extrusion process when compared to methylmercury chloride. As seen in SPMs, Ca(2+)-ATPase and 45Ca uptake in microsomes were also significantly inhibited in both cerebellum and cortex by mercury salts in a concentration-dependent manner, the effect being greater with mercuric chloride. These results indicate that both mercury and methylmercury inhibited the Ca2+ pumps located in SPMs and microsomes differentially, and to some extent the effects were also region specific.

In vitro effect of lead on Ca(2+)-ATPase in synaptic plasma membranes and microsomes of rat cerebral cortex and cerebellum

Earlier investigations from this laboratory suggest that lead interferes with the calcium homeostasis of rat brain through modulation of an inositol polyphosphate second-messenger system. The present investigation was initiated to study the comparative effects of lead chloride and lead acetate on synaptosomal and microsomal Ca(2+)-ATPase of rat cerebral cortex and cerebellum in vitro. The synaptic plasma membranes and microsomes were prepared by using sucrose gradient (1.2-0.8 M). The assay of Ca(2+)-ATPase was done by hydrolysis of ATP and the liberated inorganic phosphate was estimated. Both lead chloride and lead acetate at micromolar concentrations significantly inhibited the Ca(2+)-ATPase of synaptic plasma membranes and microsomes of cerebral cortex and cerebellum in a concentration-dependent manner. The IC50 values of Ca(2+)-ATPase for both lead salts in synaptosomes were significantly lower (P < 0.05) than that of microsomes, indicating more sensitivity. Significantly (P < 0.05) lower IC50 values for both synaptosomal and microsomal Ca(2+)-ATPase were obtained for lead acetate than for lead chloride. The results suggest that lead acetate is more potent than lead chloride in inhibiting the Ca(2+)-ATPase. The microsomal Ca2+ uptake was also studied in cerebellum and cerebral cortex in the presence of different concentrations of both the lead salts. However, these lead salts in vitro did not reveal a significant (P < 0.05) change in the microsomal Ca2+ uptake of cerebellum and cerebral cortex. But earlier investigations indicated that in vitro lead (0.25-2 microM) inhibits inositol 1,4,5-triphosphate-mediated Ca2+ uptake and release in microsomes of rat cerebellum.

Modulation of protein kinase C by heavy metals

Protein kinase C (PKC) regulates a variety of intracellular and extracellular signals across the neuronal membrane. PKC requires calcium and phospholipid, particularly phosphatidylserine (PS) for its activation. The data indicates that mercury (Hg), lead (Pb) and methyl mercury (CH3Hg) in vitro inhibited the PKC activity at micromolar concentrations in a concentration-dependent manner with IC50 values of 1.5, 2.12 and 0.22 microM, respectively. The IC50 values indicate that CH3Hg was more potent in inhibiting the enzyme activity than Hg or Pb. The basal PKC activity was also inhibited by Pb or Hg. However, the PS-stimulated PKC activity was more sensitive to Pb or Hg than the basal enzyme. The phorbol ester binding to PKC was also found to be inhibited by micromolar concentrations of these metals in vitro. Hg and CH3Hg were more potent inhibitors of phorbol ester binding than Pb. Dithiothreitol (DTT), a dithiol, but not glutathione (GSH) a monothiol, protected the activities of both PS-stimulated and basal PKC from metal-inhibition in a concentration-dependent manner. The present study suggests that the dithiols but not monothiols effectively protect metal-inhibited activity of PKC in rat brain.

In vitro interaction of heavy metals with ouabain receptors in rat brain microsomes

This study investigates the influence of heavy metals on ouabain-binding in presence of thiol (sulfhydryl) compounds. The data on in vitro effects of mercury (Hg), lead (Pb) and cadmium (Cd) showed significant inhibition of 3H-ouabain binding to microsomal membrane in a concentration-dependent manner. Maximum inhibition of 3H-ouabain binding was observed at 1 microM for Hg and 100 microM each for Pb and Cd. Preincubation with monothiol (L-cysteine or glutathione) or dithiol (dithiothreitol) protected inhibition of 3H-ouabain binding to the membranes by Hg or Pb. Dithiol but not monothiols partially protected Cd-inhibition. The present data confirm that the heavy metals interact with ouabain receptors in a manner similar to SH-blocking agents and protection of metal-inhibited 3H-ouabain binding by thiol compounds is metal specific.

Effect of mercuric chloride on the kinetics of cationic and substrate activation of the rat brain microsomal ATPase system

Mercuric chloride (HgCl2), a neurotoxic compound, inhibited the adenosine triphosphatase (ATPase) system in a concentration-dependent manner. Hydrolysis of ATP was linear with time with or without HgCl2 in the reaction mixtures. Higher inhibition of (Na(+)-K+)ATPase activity by HgCl2 was observed in alkaline (8.0 to 9.0) pH and at lower temperatures (17 to 32 degrees). Activation energy values were increased slightly in the presence of HgCl2. Activation of (Na(+)-K+)ATPase by ATP in the presence of HgCl2 showed a decrease in Vmax from 15.29 to 5.0 mumol of inorganic phosphate (Pi)/mg protein/hr with no change in Km. Similarly, activation of K(+)-stimulated p-nitrophenyl phosphatase (K(+)-PNPPase) in the presence of HgCl2 showed a decrease in Vmax from 3.26 to 1.35 mumols of p-nitrophenol (PNP)/mg protein/hr with no change in Km. K(+)-activation kinetic studies indicated that HgCl2 decreased Vmax from 14.01 to 4.30 mumols Pi/mg protein/hr in the case of (Na(+)-K+)ATPase and from 3.45 to 2.40 mumols PNP/mg protein/hr in the case of K(+)-PNPPase with no changes in Km. Na(+)-activation of (Na(+)-K+)ATPase in the presence of HgCl2 showed a decrease in Vmax from 11.06 to 3.23 mumols Pi/mg protein/hr and an increase in Km from 1.06 to 2.08 mM. Preincubation of microsomes with sulfhydryl (SH) agents dithiothreitol, cysteine and glutathione protected HgCl2-inhibition of (Na(+)-K+)ATPase. The data suggest that HgCl2 inhibited (Na(+)-K+)ATPase by interfering with the dephosphorylation of the enzyme-phosphoryl complex.

Inhibition of rat brain microsomal Na+/K(+)-ATPase and ouabain binding by mercuric chloride

This study concerned the effects of mercuric chloride on Na+/K(+)-ATPase and [3H]ouabain binding in rat brain microsomes in vitro. The data showed that HgCl2 inhibited Na+/K(+)-ATPase effectively at micromolar concentrations. The degree of inhibition was decreased with increases in enzyme concentration and incubation time. Variations in the ionic strength of Na+ and K+ did not alter the percent inhibition of Na+/K(+)-ATPase activity by HgCl2. Repeated washings partially restored enzyme activity. The binding of [3H]ouabain to microsomal membranes was inhibited by HgCl2 in a concentration-dependent manner. Cumulative inhibition studies with HgCl2 and ouabain indicated that these inhibitors did not act concurrently and independently on Na+/K(+)-ATPase.